Thermostats



May 14, 1963 c. D. FLANAG'AN THERMOSTATS Filed Aug. 12. 1960 United States Patent This invention relates to thermostats, and more particularly to snap-acting thermostatic elements.

Among the several objects of the invention may be noted the provision of a snap-acting thermostatic element constructed to provide time-current characteristics which are unusual for the class of thermostats upon which the invention is an improvement; the provision of a thermostat of the class described which is adapted for operation in electrical circuits such that under high overload currents the device will comparatively rapidly trip a circuit open and which under ultimate trip current will delay circuit opening more than heretofore; and the provision of a thermostat of the class described having a number of parameters such that it may be conveniently designed and constructed for wide variations in required time-current and other operating characteristics. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

FIG. 1 is a plan view of a thermostatic switch incorporating the invention;

FIG. 2 is a vertical section taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged detail view of portions of FIG. 2;

FIG. 4 is an isometric view illustrating a method of manufacturing a snap-acting disc made according to the invention; and,

FIG. 5 is a perspective view of a snap-acting disc made according to the invention.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawrugs.

The invention is applicable to snap-acting elements having various dished, bent, creased, dimpled and other deformations to bring about the snap action. However, since the dished form is often used, it is with respect to such that the invention Will be described for purposes of illustration, it being understood that the principles of the invention may be applied to the other forms.

Snap-acting thermostatic elements constituted by dished bimetallic discs, deformed flexible sheets and the like for circuit control and similar purposes are known; see, for example, US. Patents 2,768,342 and 2,866,039. The configurations of such snap-acting thermostatic elements result in certain time-current relationships under high overload currents and under ultimate trip currents. These relationships are diflicult to vary by design and structural changes to meet unusual specifications. By means of the present invention, a wide variety of such variations can be accommodated without substantial difficulties connected with design and construction.

Referring now more particularly to the drawings, an

example of a .typical switch to which the invention may be applied will first be described. At numeral 1 is shown a nonconductive switch housing in the form of a cup having a bottom 3 and an open top 5 adapted to receive a cover (not shown). Supported within suitable openand 4-7 on its underside.

3,089,932 Patented May 14, 1963 ings within the bottom 3 are conductive clips 7, 9 and 11. These are extended through the bottom 3 to form outside line terminals 13, 15 and 17, respectively. Two of these conductive clips 7 and '9 also form inside contacts 19 and 2 1, respectively, within the housing 1. The other conductive clip 11 carries an inside portion 23 corresponding to the contacts 19 and 21, except that the portion 23 does not act as a Contact. The members 19 and 23 form the terminals of a heater wire 25 of the resistance type made of material such as Nichrome or the like. The word Nichrome is a registered trademark of the Driver-Harris Co. for an electrical heating and corrosion-resisting alloy consisting essentially of 15%- 16% chromium; 59%62% nickel; about 24% iron and 0.1% carbon.

Threaded through a boss 27 in the bottom 3 is an adjustable support post 31 for a composite snap-acting thermostatic disc 33 made according to the invention. A desired threaded adjustment of the post may be maintained by a lock nut 35, adjustments to be accomplished by means of a flat 37. The thermostatic disc 33 is supported on the post 31 by means of a reduced extension 29 extending loosely through a central opening or hole 39 in the disc. A staked head 30 maintains the loose connection. Looseness is only suflicient to permit the disc 33 to deflect. Thus the arrangement is such that the disc is held captive on the end of the post 31 so as to permit reversal of curvature of its dished form by snap action. It is provided with a marginal notch 41 engaging loosely with a rib 43 formed on the inside of the housing 1 to prevent rotation while allowing snap-acting deflection.

The disc 33 also carries opposite welded contacts 45 The contacts 45 and 47 constitute circuit-connecting means for the disc by means of which the disc is supplied with current when contacts 45 and 47 are located in a closed circuit. The dotted lines E in FIG. 5 illustrate how current has a path of concentration of density between the contacts, it being understood that some current of smaller densities flows between contacts on both sides of the path B. These contacts 45 and 47 are established preferably on a diametral line CL. Between them is the opening 29. The so called cold position of the thermostatic element 33 is shown in the drawings, wherein movable contacts 45 and 47 engage fixed contacts 19 and 21, respectively, thus closing a connected load circuit C, for example a motor circuit. Load current will be fed in parallel through the disc 33 and heater 25 when contacts 45 and 47 engage contacts 19 and 21. Otherwise both the disc 33 and the heater are deprived of current.

Under normal load conditions the thermostatic ele ment 33 is insufficiently heated to change its downwardly convex configuration shown. It the current in circuit C becomes excessive, the temperature due to ambient temperature, resistance heating in the disc 33, and the heated wire 25 cause the element 33 to snap from the downwardly concave position shown to an upwardly concave position, thereby lifting the movable contacts 45 and 47 from the stationary contacts 19 and 21, respectively. This opens the circuit C, depriving both the element 33 and the heater wire of current. Upon cooling, the circuit may automatically reclose if the element 33 is the automatically reset type, or it may remain open until manually reclosed if the element 33 is of the manual reset type. Appropriate structural conditions for either type are known and require no further elaboration.

Ordinarily an element such as 33 is constituted throughout by a composite bimetallic sheet, such as face-bonded Invar and brass, having relatively low and high coefficients of expansion, respectively. In such case the highcoefficient brass is located on the heater side and the low-coetlicient Invar oppositely. It is in respect to a new disposition of such materials, to provide an improved element such as 33, that the invention is concerned.

Referring to FIGS. 1, 3 and 5, the element 33 according to the present invention is constituted by a composite diametrical band or strip 49 of face-bonded material cOrnponents, wherein the lower component 51 on the heater side has a relatively high coefficient of thermal expansion and the upper component 53 on the opposite side has a relatively low coefiicient of thermal expansion. Flanking the strip 49 and edge-bonded thereto are composite sheet segments 55 of facebonded components which are inversely related as regards the order of their high and low coeflicients of thermal expansion. Thus in the composite segments 55 the lower sheets 57 have the relatively low coefficients of thermal expansion and the upper sheets 59 have the relatively high coefficients of thermal expansion. Sheets 51 and 59, for example, may be composed of brass, and sheets 57 and 53 may be composed of Invar. The configuration is such that the hole 39 and the weldments of the movable contacts 43 are in and on the strip 49. Preferably, the sides of the band 49 are parallel to and equally distant from the line CL passing through the centers of the contacts 45, 47 and center of the opening 39 so as to obtain symmetrical contact action, although this is not always necessary.

To elucidate further the character of the new element 33, a method of ts manufacture is shown in FIG. 4. This illustrates an area A of material consisting of high coeflicient strips 59 flanking a central low-coeflicient strip 53', and adjacent low-coefficient strips 57 flanking a central high-coefiicient strip 51'. Flanking strips 59 are respectively face-bonded to the flanking strips 57', and central strip 53 is face-bonded to central strip 51'. Central strips 53 and 51' are edge-bonded to the flanking strips 59 and 57', respectively. The composite material thus constituting sheet A is the material from which the disc 33 is punched and dished. In FIG. 4 an appropriate location of the circular punch line is indicated at 61, the ultimate locations of movable contacts 43 are shown at 63 and the location of the hole 39 is shown at 65. The location line CL is also shown on FIG. 4.

As regards FIG. 4, the dishing after punching is accomplished so that the convex side of the resulting disc is forward and the concave side backward, as suggested by the broken line V. This results in the punched-out parts of the strips 53', 59', 51 and 57 becoming the parts 53, 59, 51 and 57, respectively, of the finished disc such as shown in FIGS. 1, 3 and 5.

The invention comprises an inversion or reversal in location of the components or relatively high and low coeflicients in the strip 49 and segments 55. The materials in the strip 49 are then according to the usual arrangement and those in the segments 55 in reverse. The amount of material which is in the reverse arrangement will determine the amount of variation from the standard time-current relationship which may be expected from a comparable conventional disc. This is because the snapacting reversal of concavity upon heating of the strip 49 tends to take place as usual; whereas heating of the segments 55 causes an opposing efiect, tending to delay any snap-acting reversal of the disc as a whole.

It will be appreciated that heating of the disc is in part by ambient heating and heat from the heater 25 which is absorbed more or less at the same rate by strip 49 and segments 55. Heating is also accomplished either by overload current or ultimate trip current flowing between contacts 45 and 47. The density of such currents is greater along the strip 49 than through the segments 55, as suggested by the path of concentration illustrated by the dotted lines E in FIG. 5. Consequently, the strip 49 will tend to heat more rapidly than will segments 55, particularly in response to higher currents, some time delay being involved before heat will progress by conduction from the strip 49 to the segments 55 through the thin bond lines therebetween. Thus on heavy overload current, the current-carrying strip 49 more rapidly reaches a higher temperature than do the segments 55. Therefore, the delaying action by the cooler segments 55 on the snap action of strip 49 is less for higher currents and more for lower currents. Consequently, as compared with action upon occurrence of ultimate trip currents, comparatively short overload tripping times will accrue. On essentially ultimate trip currents, sufiicient time will elapse for heat transfer from the strip 49 to the segments 55 to inhibit opening action of the disc. Ultimate trip current is defined as the maximum current which can be applied at a given ambient temperature to a thermostatic switching device without causing actuation or tripping thereof, or that value of current which, due to gradual temperature build-up, will trip such a device in a comparatively long specified period of time. Many conventional thermostats ordinarily provide desirable overload characteristics in normal applications, but fail to provide adequately high ultimate trip-current characteristics, which frequently results in overprotection and nuisance trip-outs in this phase of protection. The converse is also true in conventional thermostats. That is, ultimate trip characteristics can be matched to the device to be protected to avoid overprotection, but only at the risk of underprotection for current overload conditions. The instant invention uniquely permits matching the time-current characteristics of the switching device to those of the device to be protected, whereby adequate protection both on current overload and for ultimate trip conditions is afforded while at the same time avoiding overprotection for the ultimate trip condition.

The amount of material in segments 55 which is in reverse relationship to that in the strip 49 determines the variation from the conventional time-current relationships which may be expected from comparable discs. To illustrate this, two extremes in design may be conceived. The first would be one in which the strip 49 is so wide that little or no reverse bimetal is used (i.e., segments 55 very small or missing). In this case the ability of the segments 55 to modify the snap action would be nil. The second would be one in which the segments are so large and contain so much reverse composite material that there would be no thermostatic action at all. By appropriate variations between these extremes it is possible to provide a snap-acting element in which the time-current characteristics can be altered from the standard to meet a large range of application requirements.

While I have shown a configuration of the disc which is essentially full round, it will be understood that it may be of known modified forms such as a disc with ears for the contacts, cut-down marginal portions, ribbed or the like. It will also be understood that the component materials used for strip 49 need not be the same as those used for segments 55. Thus while there are required differences in the coeflicients of thermal expansion of the com ponents in strip 49 and in segments 55, these diiferences need not be equal. It is only necessary that the order of their arrangements in the disc shall be inverse or opposite. The fact that the differences need not be equal provides another design parameter which may be varied to meet required specifications.

In view of the above, it will be clear that the invention may be carried out with any appropriate materials in the strip 49 and segments 55 such as bear a generally reversed relationship to one another as regards their characteristics of high and low thermal co'efiicients of expansion, and that the segments 55 may be arranged other than symmetrically with respect to the strip 49, although the latter arrangement is preferable for an operatively balanced structure. In general, the arrangement should be such that the thermostatic force of strip 49 is primary and controls the desired movement, while the force of segace-a.

ments 55 exerts merely a modification of such primary force.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A thermostatic element comprising a flexible conductive sheet, circuit-connecting means carried by the sheet, between which connecting means current flows through the sheet along a path of density concentration when the sheet is connected in a circuit by said connecting means, said sheet along said path being composed of layers having relatively high and low coefiicients of thermal expansion in a first order, said sheet adjacent to and alongside of said path having marginally connected layers of relatively high and low coeificients of thermal expansion in an inverse order with respect to said first order.

2. A snap-acting thermostatic element comprising a flexible conductive sheet which is deformed for inherent snap action upon temperature change, spaced circuitconnecting means carried by the sheet, between which connecting means current flows through the sheet along a path of density concentration when the sheet is connected in a circuit by said connecting means, said sheet along said path being composed of layers having relatively high and low coefiicients of thermal expansion in a first order, said sheet adjacent to and alongside of said path having marginally connected layers of relatively high and low coefficients of thermal expansion in an inverse order with respect to said first order.

3. A snap-acting thermostatic element comprising a flexible conductive sheet which is deformed for inherent snap action upon temperature change, spaced circuitconnecting means carried by the sheet, between which connecting means current flows through the sheet along a path of density concentration when the sheet is connected in a circuit by said connecting means, said sheet along said path being composed of bimetallic layers having 6 relatively high and low coefficients of thermal expansion in a first order, said sheet adjacent to and along both sides of said path having marginally connected bimetallic layers of relatively high and low coeflicients of thermal expansion in an inverse order with respect to said first order.

4. A snap-acting thermostatic element comprising a flexible conductive sheet having a dished form adapted for inherent snap action upon temperature change, spaced contacts carried by the sheet on opposite sides of the dished form, between which contacts current flows across the dished form along a path of density concentration when the sheet is connected into a circuit by said contacts, said sheet along said path and within its dished -form being composed of bimetallic layers having relatively high and low coe'lficients of thermal expansion in a first order, said sheet in parts of its dished form and adjacent to and along both sides of said path having edge-bonded bimetallic layers of relatively high and low coefificients of thermal expansion in an inverse order with respect to said first order.

5. A snap-acting thermostatic element comprising a dished flexible conductive disc adapted for inherent snap action upon temperature change, spaced contacts carried by the disc adjacent opposite margins thereof, between which contacts current flows across the disc along a path of density concentration when the disc is connected into a circuit by said contacts, said disc along said path being composed of a diametral strip of bimetallic layers having relatively high and low coefiicients of thermal expansion in a first order, said sheet in parts of its dished disc form adjacent to and along opposite sides of said path in the strip having edge-bonded equal segments of bimetallic layers of relatively high and low coefiicients of thermal expansion in an inverse order with respect to said first order.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,811 Thomas Sept. 17, 1929 2,196,671 Gille et al. Apr. 9, 1940 2,675,267 Vaughan Apr. 13, 1954 2,742,547 Chang-Kaing Tsai Apr. 17, 1956 

5. A SNAP-ACTING THERMOSTATIC ELEMENT COMPRISING A DISHED FLEXIBLE CONDUCTIVE DISC ADAPTED FOR INHERENT SNAP ACTION UPON TEMPERATURE CHANGE, SPACED CONTACTS CARRIED BY THE DISC ADJACENT OPPOSITE MARGINS THEREOF, BETWEEN WHICH CONTACTS CURRENT FLOWS ACROSS THE DISC ALONG A PATH OF DENSITY CONCENTRATION WHEN THE DISC IS CONNECTED INTO A CIRCUIT BY SAID CONTACTS, SAID DISC ALONG SAID PATH BEING COMPOSED OF A DIAMETRAL STRIP OF BIMETALLIC LAYERS HAVING RELATIVELY HIGH AND LOW COEFFICIENTS OF THERMAL EXPANSION IN A FIRST ORDER, SAID SHEET IN PARTS OF ITS DISHED DISC FORM ADJACENT TO AND ALONG OPPOSITE SIDES OF SAID PATH IN THE STRIP HAVING EDGE-BONDED EQUAL SEGMENTS OF BIMETALLIC LAYERS OF RELATIVELY HIGH AND LOW COEFFICIENTS OF THERMAL EXPANSION IN AN INVERSE ORDER WITH RESPECT TO SAID FIRST ORDER. 